Safety and the law require that a motor-vehicle door latch hold the door extremely securely. To this end a heavy-duty door latch is provided which frequently locks one element on the door completely through another element on the doorpost.
In order to insure proper functioning of such a heavy-duty structure various centering devices are provided to insure that the door always assumes the exact same position relative to the doorpost when closed. Such formations normally include a pin carried on the door and a recess in the doorpost, or vice versa. Both the pin and the recess are complementarily tapered in the direction the door moves as its closes to insure accurate fitting-together of the two parts.
A problem with such an arrangement is that the door must be extremely meticulously mounted on the vehicle in order to insure proper interengagement and alignment of the various parts that allow the latch to function. Any misalignment, in particular a shifting of the door or doorposts longitudinally in the direction of travel of the vehicle, normally makes it impossible for the latch to function. Such shifting can be the simple result of wear-and-tear or the result of an accident. In either case substantial repairs must be made before the essential door latch can be used again.